First, set up the email address to forward to:

1. Log in by web browser.
2. In the left-hand navigation pane, click Notification.  In the new window, select Set Up Notification.
3. Enter the email address of your phone.  (Example: 5123456789@mms.att.net.  Different providers will have different addresses.)  
4. Click the Add button to the right.

Next, verify that forwarding is turned on:

1. Click Notification again.
2. This time, click Activate Notification.
3. If the “Notify me through Email” option is set to Off, select one of the other options.